The biggest baby boom in the UK for 40 years contributed to the country's population growing more quickly than that of any other EU country last year, according to official statistics.

The UK population reached 63.7 million in mid-2012, according to annual estimates from the Office for National Statistics (ONS), an increase of just under 420,000, or 0.66%, from a year before. This was a bigger absolute population rise than any other EU nation over the period, with France next at 319,000 and Germany seeing a 166,000 rise.

Of the population growth, 61% was due to there being 254,400 more births than deaths over the period. The total of 813,200 births was the biggest number seen in the annual ONS figures since 1972.

The remaining 39% of the increase came from net migration, with 517,800 overseas arrivals – counted in these figures as people staying in the UK for at least 12 months – and 352,100 departures.

The baby boom effect was not sudden, said Paul Vickers, a statistician at the ONS. "It's just been gradually building up over the past six years. What we've seen is that the number of nought-to-six-year-olds has actually gone up by 580,000 compared with 2001.

"But there was a low point in the number of births at the turn of the century. The number of seven-to-16-year-olds is half a million less than it was in 2001."

Such changes were down to a range of factors, he said, including shifting social attitudes to parenthood, and the effect of migration. Of births over the period in England and Wales, Vickers said, just over a quarter were to mothers not born in the UK.

Migrants were more likely to give birth mainly due to their age profile rather than cultural reasons, he added. "The key drivers for the migration are students, then workers or people who accompany workers. With that sort of demographic bulge you get more people of the 18 to 35 or 40 age group coming in – and they're the ones more likely to have children."

There are fears the baby boom could put added pressure on hospitals. Cathy Warwick, chief executive of the Royal College of Midwives, said 5,000 more midwives are needed in England to provide services for new mothers and their children.

She said: "In Scotland, Wales and Northern Ireland, births are at recent highs. Births in England are continuing to boom, with the proportion of births to the oldest women growing faster than for younger women.

"This places considerable pressures on maternity services and we are struggling to provide high quality antenatal and postnatal care.

"Despite recent welcome increases in the numbers of midwives, there is still a shortage."

A drop in the number of smokers, plus improvements to health treatments for circulatory illnesses, have seen more men living past the 75-year marker, the ONS said. The number of men aged 75 and above in the UK has increased by just over 26%, or 422,353, since mid-2001, to 2,043,034.

Separate ONS migration figures for the year to the end of September 2012 show that of the around 500,000 arrivals in that period, 190,000 came to study.

Data for 2011 showed the top five countries of origin for those arriving in the UK from abroad were India, China, Pakistan, Poland and the US.

The population increase was unevenly spread around the country, with London alone accounting for almost a quarter of the entire rise, with 104,000 more residents. Scotland and Wales saw proportional rises of 0.26% and 0.34% respectively, against 0.51% for Northern Ireland and 0.73% for England.

Not unexpectedly, London also saw the most international migrants arriving, with net migration of 69,000. The figure for Northern Ireland was 400.

In mid-2012 England had an estimated total population of 53.5 million, with 5.3 million in Scotland, 3.1 million in Wales and 1.8 million in Northern Ireland.

The population estimates, which the ONS describe as the "essential building blocks" for a series of other statistic models, show an increasingly ageing nation, with 10.8 million people, or 17%, aged 65 or over.